The name garnet comes from the Latin word granatus, meaning “seed,” because it often resembles small round seeds (similar to the red kernels of the pomegranate)when found. Garnets are isomorphous, meaning that they share the same crystal structure. This is a group of six differently colored minerals with similar crystal structures and related chemical compositions. The garnets can be divided into two series the pyrope-almandine series (“pyralspite” series) and the uvarovite-grossularite-andralite series (“ugrandite” series).
Red is the color which occurs most frequently, but there are also garnets showing different colors of green, pale to bright-yellow, fiery orange and fine earthy shades. Garnets are abundant in metamorphic rocks. Some of the best crystals are from schist, serpentines, metamorphosed limestones, gneisses, and granite pegmatites. They form under high temperatures and pressure. Garnets can be used by geologists as an indication of the temperatures and pressures at which the rock was formed.
There are six main garnet types used by the jewelry trade, they are pyrope, almandine, spessartine, grossular garnet, andradite, and uvarovite. The best known are the deep-red almandine garnet and pyrope garnets. Pyropes and rhodolites are usually free from flaws, whereas almandines are likely to contain flaws. Fine pyropes have been used as gems by royalty and the combined brilliance and fine purplish color of rhodolite have produced some exquisite transparent gemstones. In the 1960s, a new garnet was discovered which made green an important garnet color. It was named tsavorite, after the Tsavo area of southeast Kenya.
Garnet can be faceted, and those of deep color are fashioned as cabochons and are called carbuncles. Red garnets were the most commonly used gemstones in the ancient Roman world. Dark red garnet (carbuncles) was loved by Victorians.
Gem quality pyrope comes from Arizona and Utah; almandine from Alaska and Idaho; and rhodolite from North Carolina. It is also found in Australia, Ceylon, Czechoslovakia, South Africa, and South America.
Garnet is the first of the twelve gemstones of the ceremonial breastplate worn by the high priest Aaron, representing the twelve tribes of Israel as described in the Old Testament book of Exodus, and is also known as the month of the January’s birthstone.
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